TMUA sitting in october or january

hi I'm currently in year 12 and was wondering which sitting I should do. i plan to do early entry and if i apply to oxford i don't need the tmua for that so i can do either sitting, i'm just wondering if i'd be better off doing the january sitting to give me more time to prepare. but then again i'm going to spend a portion of my time everyday in the summer doing mat and tmua revision anyways, so maybe it would be better to just get it over and done with in october? after all there's only so many past papers and revision questions out there for these admissions tests, so i'm not sure what to do.